A storage apparatus is used for data preservation. The storage apparatus is equipped with a plurality of storage devices such as hard disk drives (HDDs) or solid state drives (SSDs) and makes it possible to use a storage area of a large capacity.
There is a technique that acquires a backup of data preserved in a storage apparatus. For example, a snapshot is a method for acquiring a backup. In the snapshot, when update of data is intended after a backup is acquired at a certain time point, data before the update with respect to the updated data is saved to be kept in the storage device. For example, there is a suggestion to use a differential bitmap having bits associated with blocks within a logical unit in order to manage, in units of blocks, whether or not data is saved and recorded (i.e., updated).
Also, there is a suggested technique that manages a snapshot image for each generation by preserving a snapshot image reflecting up to N generations and history information including updated data of N+1th generation, N+2th generation . . . as updated data with respect to the image.
There is also a suggested technique that builds a single file system in a consolidated storage area obtained by consolidating a first storing area and a second storing area. In the suggested technique, metadata (e.g., inode) related to a file are stored only in the first storing area when storing the file, and thus, the metadata is not newly prepared but just changed when the file is moved.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2005-301499, Japanese Laid-Open Patent Publication No. 2002-278819, and Japanese Laid-Open Patent Publication No. 2007-079774.